1. Field of the Invention
The present invention relates to a determining method and an optical touch system thereof, and more specifically, to a method of determining whether a lens device is shifted and an optical touch system thereof.
2. Description of the Prior Art
In general, a conventional optical touch system utilizes a light interruption method or a direct image capturing method to detect a position of a user's finger on a touch surface. Both of the two methods utilize lens devices (e.g. a CMOS (Complementary Metal-Oxide Semiconductor) sensor) and light sources (e.g. a near-infrared light emitting device) to perform optical positioning of the optical touch system. The aforesaid lens devices are usually disposed at upper-left and upper-right corners of a touch screen, respectively. The difference between the two methods is that the light interruption method utilizes a background lighting design, in which reflection strips are disposed around the touch screen. In the light interruption method, a user's finger is taken as an interruption object for interrupting light when touching the touch screen. At this time, a pixel position with lower brightness of an image captured by the lens device could be determined as a position of the user's finger on the touch screen. On the other hand, the direct image capturing method utilizes a light absorbing design, in which mat strips are disposed around the touch screen. In the direct image capturing method, a user's finger is taken as a reflection object for reflecting light when touching the touch screen. At this time, a pixel position with higher brightness of an image captured by the lens device could be determined as a position of the user's finger on the touch screen.
The optical positioning accuracy of the aforesaid two methods depends on whether an image capturing range of the lens device covers the whole the touch surface. However, offset of an optical axis of the lens device from its original position usually occurs due to some factor (e.g. the optical touch system receiving sudden impact or poor assembly of the optical touch system). The aforesaid problem may cause incorrect optical positioning of the optical touch system.